Isobutylene-based terpolymers including isoolefin, styrenic, and multiolefin derived units have been disclosed in U.S. Pat. Nos. 3,948,868, 4,779,657; and WO 01/21672. Compositions useful for air barriers such as innerliners and innertubes which include such terpolymers are not known.
Improving the specific properties of tire innerliners without sacrificing current performance is desirable. Use of isobutylene-based elastomers such as butyl rubber (IIR), halobutyl rubbers (chloro (CIIR) or bromo (BIIR)) or brominated isobutylene-co-p-methylstyrene (BIMS) as the innerliner polymer serves to provide for decreased permeability to air compared to general purpose elastomers (such as NR, BR, or SBR) or their blends with isobutylene elastomers. Flex fatigue resistance, adhesion to other tire components such as carcass and bead compounds, and abrasion resistance are also desirable performance properties. Use of BIMS copolymers increases the compatibility of the innerliner with GPR hydrocarbon elastomers; however, co-vulcanization using sulfur cure systems is still not achieved to a sufficiently high degree. Improved lab adhesion values to carcass compounds is still desirable.
To be useful in, for example, a tire tread or tire sidewall as part of a multi-component automobile tire, the terpolymer must desirably be both sulfur curable, and compatible with other rubbers such as natural rubber and polybutadiene. Further, in order to serve as an air barrier such as a tire innerliner, the terpolymer compositions must be air impermeable, adhere well to the tire carcass such as a poly(styrene-co-butadiene) (SBR) carcass, and have suitable durability. These properties are often difficult to achieve together, as improving one can often diminish the other.
It is unexpected that the incorporation of a multiolefin derived unit in a composition including a polymer having a isobutylene/p-methylstyrene backbone would contribute to both improved carcass adhesion and flexibility, while maintaining air impermeability. Likewise, it is unexpected that such terpolymer will sulfur cure in light of the IB/PMS copolymers failing to sulfur vulcanize. Yet, the inventors here demonstrate, among other things, the practical use of certain isoolefinic terpolymers that incorporate multiolefins that are sulfur curable. More particularly, it has been discovered that these terpolymers are useful in curable blends with suitable fillers and the like due to improved traction and abrasion performance, thus making these compositions useful in tire treads, sidewalls as well as air barriers such as innerliners and innertubes for pneumatic tires.
Other background references include U.S. Pat. Nos. 3,560,458 and 5,556,907 and EP 1215 241 A.